Q&A 337.2
Why must some medicines be taken when the stomach is empty?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
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Date prepared: 11th October 2012
Background
The instructions on some medicines state that they must be taken “before food” or “when your stomach is empty”. Why is this? Does it matter if people do not do this?
Answer
It is possible to find out whether a medicine needs to be taken when the stomach is empty by checking the electronic MedicinesCompendium (eMC) for the manufacturer’s patient information leaflet (PIL) or summary of product characteristics (SPC) (1). Appendix 3 of the British National Formulary (BNF) also has a list (2).
Most of the medicines that must be taken when the stomach is empty are not absorbed into the bloodstream very well if there is food and acid in the stomach. Some common examples include:
azithromycin tablets or capsules
flucloxacillin
oxytetracycline.
These medicines should be taken an hour before food, or two hours after food. This will allow them to be absorbed when the stomach is empty. If this is not done then the medicine will not be as effective, so people should be encouraged to follow the instructions carefully.
The group of medicines called bisphosphonates, some of which are used to treat osteoporosis, are a particular problem, and even the smallest amount of food has a very significant effect. They include:alendronic acid, disodiumetidronate, ibandronic acidandrisedronate sodium.Bisphosphonates should not be taken at bedtime. These medicines should generally be taken first thing in the morning before breakfast as follows (1):
Alendronic acid
/ Take at least 30 minutes before the first food, drink, or other medicines of the day with a full glass of plain water.Disodium etidronate / Take at the mid-point of a 4-hour fast i.e. 2 hours before and 2 hours after food. Take with a glass of plain water.
Ibandronic acid / Take after an overnight fast (at least 6 hours).Take at least 30 minutes (ibandronic acid 50mg) or one hour (ibandronic acid 150mg) before the first food, drink or another medicine of the day. Take with a full glass of plain water.
Risedronate sodium / Take at least 30 minutes before the first food, drink or other medicine of the day. N.B. Risedronate 5mg and 30mg tablets (for daily use) can be taken at the mid-point of a 4-hour fast i.e. 2 hours before and 2 hours after any food, drink or other medicine, at any other time of the day. Take with at least one glass of plain water.
Some medicines which actually operate in the gut itself will not work if they are taken after food. Sucralfate, for example, ‘coats’ ulcers to heal them. It must be taken at least an hour before eating or it simply coats food instead and the treatment does not work. Mebeverine is used to reduce bowel spasm at meal times. It should be taken 20 minutes before meals, to enable it to start working before food arrives. Similarly, sodium cromoglicate capsules are taken before meals to minimise the effects of certain types of food allergy.
Summary
For medicines that require administration when the stomach is empty in order to be absorbed properly, people should choose times of the day that are convenient to them.
Once daily medicines are best taken before breakfast, but other good times include mid-morning, mid-afternoon and last thing at night. Bisphosphonates should not be taken at bedtime.
Some medicines need to be taken just before meals or they will not work.
Not following these instructions for the occasional dose is unlikely to be a problem, but doing it all the time may mean that the medicine does not work.
Limitations
This Medicines Q&A contains examples of common situations but is not comprehensive.
References
- Manufacturers’ Patient Information Leaflets for various products. Accessed on 15th October 2012.
- Appendix 3: Cautionary and advisory labels for dispensed medicines. Joint Formulary Committee. British National Formulary. London: BMJ Group and Pharmaceutical Press. Electronic edition. Accessed via on 11th October 2012.
Quality Assurance
Prepared by
Kate Pickett, Medicines Q&A Pharmacist (based on earlier work by Dr Simon Wills and Katie Taylor), Wessex Drug and Medicines Information Centre, University Hospital Southampton NHS Foundation Trust
Date Prepared
11th October 2012
Checked by
Sue Gough, Critical Evaluation Pharmacist.Wessex Drug and Medicines Information Centre, University Hospital Southampton NHS Foundation Trust
Date of check
18th October 2012
Search strategy
In-house texts.
Personal knowledge of in-house medicines information experts.
1
From the NHS Evidence website